1. Field of the Invention
The present invention relates to a manufacturing apparatus of polycrystalline silicon that products rods of polycrystalline silicon by depositing polycrystalline silicon on surfaces of heated silicon seed rods.
Priority is claimed on Japanese Patent Application No. 2008-231163, filed Sep. 9, 2008, the content of which is incorporated herein by reference.
2. Description of the Related Art
Conventionally, a manufacturing apparatus of polycrystalline silicon by the Siemens process is known. In the manufacturing apparatus of polycrystalline silicon by the Siemens process, a plurality of silicon seed rods are provided in a reactor and heated. Raw-material gas including chlorosilane gas and hydrogen gas is supplied into the reactor and in contact with the heated silicon seed rods, so that polycrystalline silicon is deposited on the surface of the silicon seed rods by thermal decomposition and hydrogen reduction of the raw-material gas.
In this manufacturing apparatus of the polycrystalline silicon, the silicon seed rods are fixed on electrodes provided on a bottom plate portion of the reactor so as to stand on the electrodes. Electric current is supplied to the silicon seed rods via the electrodes, so that the silicon seed rods are heated by the electric resistance. The raw-material gas is blown up from below and in contact with the silicon seed rods. As a result, rods of polycrystalline silicon are manufactured. The electrodes which hold the silicon seed rods are distributed across the inner-bottom surface of the reactor. For example, as disclosed in Japanese Unexamined Patent Application, First Publication No. H08-45847, a base plate (i.e., a bottom plate portion) having through-holes is provided in a deposition apparatus (i.e., a reactor). Electric lead portions are fixed in the through-holes so as to be surrounded by circular insulators. Electrode holders are attached to the electric lead portions. Graphite electrodes are held on the upper end portions of the electrode holders.
In a process of depositing polycrystalline silicon on the surfaces of the silicon seed rods by reacting the raw-material gas in the reactor, the deposited polycrystalline silicon reach several tens of kg by continuation of the reaction, and may peel off due to self weight. In this case, the fallen polycrystalline silicon may damage a furnace floor of the reactor, or may short-circuit between the electrodes and the furnace floor, so that the reaction is prevented from continuing.
Especially, in the apparatus of JP'847, the electrode holders are cooled since the electric lead portions are cooled. Therefore, the graphite electrodes are cooled, so that the temperature of the lower end portions of carrier members (i.e., silicon seed rods) are down. As a result, polycrystalline silicon is not deposited enough on these portions.